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How to Caulk Outside Windows with a Brick Surface

A close-up of a typical British residential house with small entrance garden and red brick exteriors.

When properly applied to your exterior brick walls, caulking looks great, seals air gaps around your window, and repels moisture for years. Here's how to DIY this, making it look like a pro did the job.

Caulking the exterior of your windows is one of those popular DIY tasks that sounds easier than it actually is. You just run a bead along the gap and boom, you’re finished! Right?

Well, if you want to get good-looking caulking that will withstand time and weathering, it takes a little more work. So what’s the secret to how to caulk windows outside on brick? You just need the right preparation, supplies, and technique.

The Basics

A grey caulk in old window casement with bare wood windowsill for winterizing to keep out cold drafts.

Caulk is a flexible putty that hardens after application. This putty is applied in a long bead with a caulking gun. It is then smoothed down while still soft.

You’ve probably seen stripes of caulking around windows before. Caulk is typically white or clear, but other colors are available. It can be applied anywhere you need a seal. Caulk is often used to keep out wind and moisture, seal down roof tiles, or cover unsightly gaps and nicks in the walls and floors.

Colors

Application of white caulk on a wooden surface.

White and clear are common options. However, you can get it in other colors. Some caulk formulas may even be mixed with latex paint, creating an exact shade match to your painted walls. Others are tinted and even textured to blend in with wood floors or panels.

Formulas

There are a number of different kinds of caulking compounds out there. These run a wide range from asphalt-based, for sealing down asphalt roof shingles, to fireproof or polyurethane foam caulks that can be used around your home’s electrical outlets.

You’ll want to get the right formula for the job. For outdoor windows, look for caulking that says ‘for exterior surfaces’ on the box. If you aren’t sure which one to get, you can always ask a store employee for advice.

Caulk for outdoor use is formulated to adhere to both brick and the window, resist foul weather, and not break down in sunlight. Some common options include:

Acrylic Caulk

Red Devil 084640 Window & Door Siliconized Acrylic Caulk, 10.1-Ounce, Dark Brown
Click image for more info

This formula, sometimes called acrylic latex, is flexible, durable, and adheres well. It’s a good all-round choice for gaps of ¼ inch or less. However, avoid the suspiciously cheap options here. They don’t last as long. Repairing later water damage will quickly eat up what little you saved in the short term.

Polyurethane Caulk

Loctite PL S40 White Window, Door and Siding Polyurethane Sealant 10-Ounce Cartridge (1618182)
Click image for more info

This sticks better and lasts significantly longer than acrylic, sometimes 20 years. Why isn’t it the top recommendation? Polyurethane is noticeably harder to work with, from application to smoothing to clean-up. However, if you have previous experience with caulking exterior windows, this is a solid option.

Latex Silicone Caulk

Dap Inc 18425 10.1 oz. Alex Fast Dry Acrylic Latex Caulk Plus Silicone - White - 12 Pack
Click image for more info

Latex caulk breaks down in sunlight, heat, and cold. Silicone caulk can’t be painted on or used on masonry. Separately, they aren’t appropriate for outdoor jobs. However, caulk formulas that combine the two can be used outside. The resulting blend is flexible, durable, and can be painted over. This is good news if you’re trying to match the caulking to your colorful window frames.

Why is it Necessary to Caulk Your Exterior?

A man on a ladder caulking the outside window.

There’re two answers to this question: moisture and airflow. Water vapor can make its way into your walls via gaps around your window frames, and rain can drip to your floors. Over time, this leads to progressive water damage that can rot your studs, crumble your plasterboard, and promote mold growth around the home.

Meanwhile, a drafty house isn’t just uncomfortable in the wintertime. It allows allergens to blow inside during pollen-heavy days. These drafts also contribute to your heating and AC bills, as your HVAC system has to struggle under the extra load of the Great Outdoors.

Finally, but not strictly necessary: a well-applied, regular line of caulk around the windows just looks better than an uneven gap. It emphasizes the lines of the house, increases curb appeal, and in general, creates a smart appearance that any homeowner can be proud of.

Why Not?

Caulking isn’t the best option for every situation. It can be used to seal gaps of up to about ½ inch, but you’ll struggle to apply most kinds of caulk to larger spaces. If you have a very wide gap, you may be better off with expanding polyurethane foam. This swells up to fill the space. You might also consider fitting a narrow strip of the board into the gap. This will seal the bulk of the space. You can go on to caulk over the small cracks around the board.

What if you have a pesky air draft or rain is getting in through your old, damaged caulk? If your forecast is bad weather for the coming weeks, you may not be able to apply new caulk for some time. What can you do? Sealant tape may be the solution. This is not a permanent fix as the adhesive will slowly but surely fail. However, it can buy you time and short-term peace of mind.

Peel-and-stick trim is another short term option. This creates a waterproof barrier and also offers some insulation. Trim of this style may be a good choice for wider gaps or areas where a long strip of the old caulk has fallen out.

How to Caulk Windows Outside on Brick

A silicone gun on a wooden surface.

You will need

  • A heat gun (highly advised)
  • A putty knife, paint scraper, or similar tool
  • A dry paintbrush or clean rag
  • Masking tape
  • Old newspaper or plastic sheeting
  • Enough caulk for the job (overestimate a little)
  • A caulking gun
  • Paper towels

You may need

  • A plastic spoon
  • For big gaps: a ¼ or ½ inch foam backer rod
  • For polyurethane caulk: mineral spirits and latex gloves
  • For other caulk formulas: sponges and water

Caulking in 10 Steps

1: Plan Ahead

A hand peeling away the stormy picture over the sunny picture.

Gather your supplies (listed above). Next, check the forecast. Are the temperatures going to be in the right range? Is rain, fog, or other wet weather expected? All of this can make your project more difficult than it has to be.

You’ll want to check the extended forecast, too. Some caulk, such as polyurethane-based formulas, can take over a week to dry! A misty morning may not ruin your newly applied caulk, but a summer thunderstorm with wind-driven rain certainly could. Figure out your timing so you don’t end up wasting your effort and supplies.

2: Remove the Caulk

If you are replacing old or damaged caulk, you need to start out with a clean surface. Caulking over old material is a recipe for seal failure. Moisture and mold may have gotten in around the old caulk, and the worn-out material will continue to crack and curl. This will damage the layer you put on top. Save yourself an expensive headache and start with a clear slate!

Old caulk that is in very bad condition may be simply peeled off with your fingers. However, it’s unlikely that 100% of it will come off. If that’s the case, or if you can’t peel it at all, consider using a heat gun. Heating the caulk makes it more flexible and easier to remove.

Next, grab your putty knife and get scraping. If you’re removing caulk that touches window glass, be careful how hard you press. Work your scraper into every nook and cranny. Don’t forget about the mortar between the bricks.

3: Prepare the Surface

Hand in rubber protective glove with microfiber cloth wiping the wooden corner of the door.

If you’re caulking against a windowpane, get it clean with some window cleaner and a microfiber cloth. Let it dry before applying caulk. It shouldn’t take long.

For the frame and brickwork, give it a good rub down with a dry paintbrush or clean shop rag to clear away any dust and particles. Then do a quick visual inspection. If there’s minor damage to the mortar or bricks has been revealed by removing the caulk, this is a good opportunity to patch that and let it cure.

Finally, if you’re planning to caulk over a large gap, consider pushing a foam backer rod into there. This reduces the amount of caulking material that you’ll need to squeeze in. It also gives the caulk something solid to cling to, so the bead won’t just sag or drop out.

4: Protect the Area

Caulking can be a messy job. Any drips that hit your bricks or window will need to be cleaned up. You can spare yourself a long, annoying task of cleaning up stray drops by protecting your work area. Use masking tape to mark out the edges of where you’ll be working. Tape on old newspapers over the window, along the windowsill, etc.

5: Prepare Your Caulking Gun

A white silicone sealant cartridge and yellow-black sealant gun.

If it’s a brand-new caulking gun, test the slide and give the trigger or lever a few squeezes. Is everything working smoothly? Great!

Next, snip the tip-off of the tube of caulk. Some come with marked cut lines, telling you where to cut to create a bead of the right width. If not, start small and test it on a scrap of wood. Nip more of the tip-off until you have gotten it wide enough. Take your time here; you can always cut more but you can’t narrow the tip back down.

Finally, open up the caulking gun and put the tube inside. Squeeze the trigger repeatedly until the tube is held snugly and the bead starts. Now you’re ready to go.

6: Apply the Caulk

Put the tip to the edge of the gap. Use your dominant hand to hold the gun and smoothly squeeze the trigger. Your other hand can support the barrel near the tip. As you work, watch to make sure that the bead is adhering to the gap’s sides. It should also be sticking to the foam backer rod if you’re using one. Move at a slow, steady pace to help ensure an even width of the bead.

Don’t be a hero and try to do the whole window in one swoop. You’ll end up with different widths of caulk when you shift your body’s position. The corners may not stick well, leaving you with gaps. You can also get bumps in the material when you squeeze the trigger.

Instead, try to do about half of a line at a time. Overlap the caulk slightly as you go. This thicker overlap will disappear in the next step.

7: Smooth Out the Caulk

A hand applying caulk to the window's edge.

It’s time to smooth down that raised, sometimes uneven bead of caulk. Do this step ASAP, before the caulk has time to start drying down.

Sure, you can use tools like spoons or dowels. However, your fingertip works just as well. Run it along the top, touching the sides of your finger to the edges of the brick and frame. Every so often, wipe off the excess on a paper towel. This creates a curve in the caulk that looks neat and repels moisture. It also gives you one last chance to seal any tiny gaps and create good contact deep inside the gap you’re sealing.

However, the ‘finger’ method doesn’t always work. Here are a few other options:

For gaps wider than your finger, try using a plastic spoon.

If you have large breaks in the caulk, you won’t be able to seal them just by moving extra material around. Break out the caulking gun and add a little extra there. Then try sealing again.

Polyurethane caulk is highly sticky, so don’t mess with it with your bare hands. Wear a latex glove. Dip your finger in mineral spirits. Now you should be able to smooth it down without a sticky disaster.

8: Clean Up

Do you have any ragged edges? Any lumps of caulk that got pushed to the side? Scrape them away now to create a clean finish.

If caulk got on your window glass, wipe it away with a damp sponge. If it’s too dry, you can scrape it off with a blade. Be careful and handle your knife responsibly.

Peel away your masking tape now, while the caulk is wet. This way, if there’s any accidental overlap with the caulk, it will still lift away. If you wait until it’s dry, your tape and scraps of yesterday’s paper may become a permanent part of your architecture.

9: Let It Cure

Installing plastic window in brick house with caulking gun foam insulation.

Happy with the look of your caulk? It’s time to leave it alone. Some formulas can feel dry to the touch in under an hour. However, it is not fully set. Impacts, errant water sprayed from a garden hose, and more can undo all of your hard work.

Acrylic-based caulks take about 24 hours to dry. Their silicone cousins may take 48 hours. Meanwhile, for highly durable polyurethane caulks, you could be looking at 3 to 10 days. The caulk tube should tell you exactly long the dry time is.

10: Final Check

Your project is almost done, with just one last detail to go. Give the caulking a final inspection. Inside, try holding tissue or a lit candle near the caulked seam. It should flutter if there is a hidden gap letting air through.

Next, head outside and give the window a good look. If you have some ragged or raised bits of dry caulk, you may be able to trim them down with a blade. Work slowly and carefully so you don’t peel the rest of caulk away. If you have any small gaps or missed spots, you can reapply a bit of caulk there to complete the seal.



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